Missing Supernova

Most supermassive stars end in a supernova, or a violent eruption of energy that results in a neutron star or a black hole, depending on the mass. If we get lucky, we can spot a supernova and then backtrack through image catalogues to see the star it came from. Thus far, we have found supernova for all types of masses, but nothing above 17 solar masses. Why are we not seeing them? After all, they should have a great potential for a large visual brightening. As It turns out, they might be so large that the explosion creates a black hole which eats up material too fast for it to radiate back to us. Normally, neutrinos in the core build up and are released as the black hole forms, but with failed supernova the singularity is powerful enough to eat this initial vanguard, removing the main force behind the supernova blast. We would call such an event a failed supernova, as you may imagine. They would be more efficient than a typical supernova because less material would be blown away and instead would be consumed by the newly-formed black hole, leading to more massive candidates. So how will be able to find these missing supernovas? By looking at archived images and looking for red supergiants that are now missing, we would have a possible failed supernova candidate (Billings 26, Howell, Cain).

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The Hunt

Chris Kochanek and his team at Ohio State University are on such a hunt. In 2014, using the Large Binocular Telescope Observatory in Arizona, Kochanek and company along with Jill Gerke and Kris Stanek found a possible failed supernova candidate in NGC 6946: a red supergiant named N6946-BH1. It is about 25 solar masses and got 1 million times brighter than the sun in from March to May of 2009 (possibly from gravitational energy), then…disappeared except for some faint infrared signals in the general vicinity No dust cover can account for the data seen, but a newly formed accretion disc from a black hole can. A separate team led by Thomas Reynolds, Morgan Fraser, and Gerard Gilmore (all a part of the University of Cambridge) looked at archived Hubble data of NGC 3021 and found another possible failed supernova. However, it should be noted that such candidates may just be stars that are now obscured by dust or have a large surface fluctuation, but X-ray data that can then be compared to black holes should reveal if they are a player here. Initial projections based on candidates seen indicate that as much as 10 to 30 percent of massive stars end their life as a failed supernova, which matches the expected missing number astronomers were looking for. Stay tuned (Billings 27, Carpineti, Crockett, Myers, Mcrae).

Another avenue for potentially detecting these failed supernovas would be neutrino bursts. Normally given off by standard supernova, these bursts would have a tell-tale signature unique to a failed scenario and depending on the size of the detector could have 1 to 2 detected a century with a maximum distance of 13 million light years away. This is because the flux, or particle hits per unit area, decreases as the objects distance increases and after a certain distance will become indistinguishable from background noise. Another difficulty would be that the burst duration is expected to be less than a second long but the energy signature should fit firmly in the 56 MeV area (Voisey).